The present invention is related to a multi-layered ceramic capacitor (MLCC) mounted on a substrate wherein the MLCC provides self-damping properties. More specifically, the present invention is related to an MLCC, or array of MLCC's, in a circuit wherein elements of the MLCC are out of electrical phase thereby providing damping of microphonic noise.
MLCC's manufactured with polarized dielectrics, such as barium titanate, are prone to microphonic noise. Microphonic noise is believed to be caused by electrostriction, as well as the piezoelectric effect, which are related to the movement of ceramic that occurs in the presence of an applied electric field. The ceramic movement can be transferred to the circuit board, on which the component is mounted, as vibrational energy ultimately producing an audible noise when electric field is applied. With leadless capacitors mounted on a circuit board microphonic noise is significantly enhanced which limits their application, particularly, in portable devices such as cell phones and the like.
Microphonic noise is a particular problem with alternating current (AC) systems as the microphonic noise tends to occur at the frequency of the AC signal, 60 Hz for example, or other vibrational frequencies and the vibration of the dielectric is transferred to the substrate and surrounding components thereby providing an audible noise. This is a particular problem in small devices and especially in devices such as headphones, devices intended for playing music and the like.
The art has primarily focused on reducing microphonic noise by physical structural alterations wherein the MLCC is mounted to the substrate in a manner suitable for eliminating, or reducing, transfer of the vibrational energy to the substrate. While somewhat successful, structural techniques designed to minimize transfer of vibrational energy do not eliminate the generation of microphonic noise and therefore the problem is not completely solved. When multiple devices are in phase the microphonic noises may be summed, or may generate harmonics, and therefore the noise is still generated even if the transfer is muted.
The present invention provides an MLCC array wherein the microphonic noise is dampened internally thereby eliminating the physical constraints related to structural techniques as typically practiced in the art. By damping the microphonic noise internally the MLCC can be surface mounted thereby significantly increasing the flexibility of design.